I had one done,the plungers seized. I don't recamend doing it. But if you do,make sure the plungers have 2 groves in the center. This should help at keeping them lubed.
I used nickle wire,it dosent crack, but get porosity sometimes. Also preheated alittle. I probably wont weld another main crack . Took lots of filing to get the cap to fit right.
The stock pistons got shaved .040, getting custom Cometic gaskets. Using the smallest precups , combined with 311 nozzles @ at least 3000 psi pop pressure. And the little .290 pump,which should easily pump enough of fuel for 400 hp. Also planing on a center mount turbo.
2250 psi is not really that high. I will be building a set here soon at 3200 psi or higher. The only downside is no hot starts,if the head and rotor are worn.
Your forgetting about the optimizer cam,I have one someware. I recall that it was not the same as the regular 6.2/6.5. Do you have the p400 cam part number ?